1. Field of the Invention
The present invention relates to a golf club shaft and more particularly to a golf club shaft in which the center of gravity of the head is lowered in such a way as to maintain the strength of the shaft at its tip side on which a head is mounted and which is flexible to fly a golf ball at a large elevation angle.
2. Description of the Related Art
In recent years, a golf club shaft composed of a reinforcing fiber such as a carbon fiber having a high specific strength and a high specific rigidity is manufactured and commercially available. As the specific strength and the specific rigidity of the carbon fiber become higher, a lightweight golf club shaft can be manufactured.
To allow the golf ball to fly in a high trajectory, there is a tendency that the center of gravity of the head is located at a lower position thereof and that the neck (portion on which shaft is mounted) of the head is short and thin. As the neck becomes short and thin, a higher stress is applied to the tip side of the shaft. Therefore it is very important that the tip side has a high strength.
If the diameter of the shaft at it tip side to increase the strength of the tip side, the degree of the flexural rigidity of the shaft becomes high, which causes the golf ball to fly in a low trajectory. Therefore there is a decrease in the effect to be brought about by lowering the center of gravity of the head to fly the golf ball in a high trajectory.
To enhance the torque strength (torsional rigidity) at the tip side of the shaft, a shaft is proposed as disclosed in Japanese Patent Application Laid-Open No. 9-234256. The shaft has the fiber reinforced resin sheet disposed at both the tip side on which the head is mounted and the butt side on which the grip is mounted. The reinforcing fiber of the fiber reinforced resin sheet forms an orientation angle of 35° to 45° with respect to the axis of the shaft. The fiber reinforced resin sheet, parallel with the axis of the shaft, forming the straight layer is also disposed at the central portion of the shaft. The region having a high torsional rigidity is formed at both the tip side and the butt side. The region having a high flexural rigidity is formed at the central portion of the shaft.
A tubular member for use in a golf club shaft is disclosed in Japanese Patent Application Laid-Open No. 2000-263653. In the tubular member, the fiber reinforced resin sheet having a low elasticity is used over the entire length of the shaft. More specifically, the tubular member is entirely composed of the fiber reinforced composite material having a high torsional strength.
In the shaft disclosed in Japanese Patent Application Laid-Open No. 9-234256, although the angular layer is disposed at the tip side to enhance the torsional strength of the shaft, the shaft is incapable of flying a golf ball in a high trajectory. In the case where the diameter of the tip side is enlarged to lower the center of gravity of the head, the torsional rigidity of the tip side becomes large. Thus the shaft is incapable of flying the golf ball in a high trajectory.
The tubular member disclosed in Japanese Patent Application Laid-Open No.2000-263653 has little effect for flexing and twisting the shaft because the fiber having a low elasticity is disposed over the entire length of the shaft. Therefore the shaft composed of the tubular member is incapable of increasing the flight distance of the golf ball. Further the shaft has a bad flying-distance capacity and a bad directional property gives a bad feeling to a golf player.